Data processing: vehicles – navigation – and relative location – Vehicle control – guidance – operation – or indication – Indication or control of braking – acceleration – or deceleration
Reexamination Certificate
2000-09-08
2003-08-12
Louis-Jacques, Jacques H. (Department: 3661)
Data processing: vehicles, navigation, and relative location
Vehicle control, guidance, operation, or indication
Indication or control of braking, acceleration, or deceleration
C701S088000, C701S090000, C701S092000, C180S248000, C180S249000, C477S035000, C477S080000, C477S084000, C477S085000, C477S904000
Reexamination Certificate
active
06606549
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a drive-force distribution controller for a four-wheel-drive vehicle, and more particularly to a drive-force distribution controller for a four-wheel-drive vehicle which can distribute proper drive forces to front and rear wheels in accordance with traveling conditions of a vehicle to thereby improve traveling stability and steering feel.
2. Description of the Related Art
Conventionally, there has been known a drive-force distribution controller for a four-wheel-drive vehicle which variably controls the engagement force of a torque distribution clutch in accordance with the difference in rotational speed between front and rear wheels.
FIG. 1
shows an exemplary control map used in such a drive-force distribution controller for a four-wheel-drive vehicle. In
FIG. 1
, the vertical axis represents engagement force T, and the horizontal axis represents rotational speed difference &Dgr;N between front and rear wheels.
At the time of acceleration and starting on a so-called low-&mgr; road such as a snow-covered road or an icy road, acceleration or starting can be effected in a stable manner if the engagement force T is rendered large at the time of acceleration or starting through employment of a mapping curve B indicated by a chain line in FIG.
1
.
However, increased engagement force makes it difficult to absorb a rotational speed difference produced between the front and rear wheels while a vehicle travels around a tight corner or is being parked or put into a garage with a large steering angle, resulting in occurrence of a so-called tight-corner braking phenomenon (in which turning becomes difficult as if brakes were being applied), and possible stalling of the engine.
This problem may be solved though employment of the mapping curve B which sharply increases the engagement force as the rotational speed difference &Dgr;N increases, and a mapping curve C which moderately increases the engagement force as the rotational speed difference &Dgr;N increases as shown in FIG.
1
. These mapping curves B and C are selectively used depending on whether the rotational speed difference &Dgr;N between the front and rear wheels is produced due to starting of the vehicle on a low-&mgr; road or acceleration, or due to traveling around a tight corner. However, it has been difficult to judge whether the rotational speed difference &Dgr;N between the front and rear wheels is produced due to starting of the vehicle on a low-&mgr; road or acceleration, or due to traveling around a tight corner. In order to solve this difficulty, there has been proposed a technique in which steering angle is detected by use of a steering angle sensor, and when a steering angle greater than a predetermined value is detected, a vehicle is judged to be traveling around a tight corner or in a tight-corner traveling mode. Further, there has been proposed a technique in which the amount by which an accelerator is depressed is detected by use of an accelerator sensor, and when an accelerator depression amount greater than a predetermined value is detected, the vehicle is judged to be accelerating or in an acceleration mode.
However, provision of the steering sensor and the accelerator sensor increases cost, which is undesirable.
Therefore, when use of the steering sensor and the accelerator sensor must be avoided, the conventional drive-force distribution controller for a four-wheel-drive vehicle uses a mapping curve A which is shown by a solid line in FIG.
1
and which has a slope between that of the mapping curve B, which sharply increases the engagement force with increase in the rotational speed difference &Dgr;N, and that of the mapping curve C, which moderately increases the engagement force with increase in the rotational speed difference &Dgr;N.
However, since the mapping curve A used in the conventional drive-force distribution controller for a four-wheel-drive vehicle is between the mapping curves B and C, a large engagement force cannot be obtained at the time of starting on a low-&mgr; road or at the time of acceleration, so that wheels which receive the distributed drive force easily slip or spin out. Further, the above-mentioned tight-corner braking phenomenon easily occurs when the vehicle travels around a tight corner at low speed or is parked or put into a garage.
That is, the conventional drive-force distribution controller for a four-wheel-drive vehicle cannot determine whether a rotational speed difference &Dgr;N is produced between the front and rear wheels due to either acceleration or starting, or due to traveling around a tight corner, and therefore cannot finely control the engagement force of the torque distribution clutch in accordance with the traveling conditions of the four-wheel-drive vehicle. Accordingly, the drive-force distribution controller cannot improve traveling stability and steering feel.
SUMMARY OF THE INVENTION
In view of the foregoing, an object of the present invention is to provide a drive-force distribution controller for a four-wheel-drive vehicle which can finely control the engagement force of a torque distribution clutch in accordance with the traveling conditions of the four-wheel-drive vehicle to thereby improve traveling stability and steering feel.
The present invention provides a drive-force distribution controller for a four-wheel-drive vehicle in which drive force produced by a prime mover is transmitted directly to front or rear wheels and is transmitted to the remaining wheels via a torque distribution clutch, and the engagement force of the torque distribution clutch is controlled in accordance with traveling conditions of the vehicle. The drive-force distribution controller comprises a calculation unit for calculating variation per unit time in rotational speed difference between the front wheels and the rear wheels; and a control unit for controlling the engagement force such that the engagement force increases as the variation per unit time in the rotational speed difference increases.
The calculation unit calculates variation per unit time in the rotational speed difference between the front wheels and the rear wheels; i.e., acceleration of the rotational speed difference. The acceleration of the rotational speed difference becomes large when the vehicle starts on a low-&mgr; road, such as a snow-covered road or an icy road, or starts abruptly, and becomes small when the vehicle travels around a tight corner or is parked or put into a garage with a large steering angle.
The control unit controls the torque distribution clutch such that the engagement force increases as the variation per unit time in the rotational speed difference increases, as calculated by the calculation unit.
In other words, the control unit increases the engagement force when the vehicle starts on a low-&mgr; road, such as a snow-covered road or an icy road, or starts abruptly, because the acceleration of the rotational speed difference becomes large in such a state.
Accordingly, the ratio of distribution of drive force to wheels which are not connected directly to the prime mover (i.e., wheels which receive a portion of the drive force) can be increased, which enables stable starting and acceleration while preventing slippage of the wheels.
In contrast, the control unit decreases the engagement force when the vehicle travels around a tight corner or is parked or put into a garage with a large steering angle, because the acceleration of the rotational speed difference becomes small in such a state.
Accordingly, the rotational speed difference between the front and rear wheels can be absorbed, whereby occurrence of the above-mentioned tight-corner braking phenomenon can be prevented.
Preferably, the control unit controls the engagement force in accordance with the rotational speed difference, as well as variation per unit time in the rotational speed difference. More preferably, the control unit comprises a control map for determining the engagement force in accordance with the rotational speed diffe
Murakami Tsuyoshi
Shigeta Ryohei
Broadhead Brian J.
Louis-Jacques Jacques H.
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
Toyoda Koki Kabushiki Kaisha
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